Electric shavers may have one or more rotatory cutter elements which may be driven in an oscillating or a continuous manner by an electric motor connected to the rotatory cutter elements through a drive train transmitting the rotation of the motor shaft to the rotatory cutter elements.
In cutter heads having a plurality of cutting rotors, the driving motion of the motor shaft of the electric motor needs to be distributed to said plurality of cutting rotors what can be achieved by a drive train having a common input element and a plurality of output elements connected to said common input element by means of transmission elements such as meshing gears, chain drive elements or belt drive elements. However, the higher the number of cutting rotors in the cutter head, the more complex the drive train and the higher the number of drive train elements. This may cause problems with accommodating the drive train elements in the cutter head which should have a small size to allow for easy handling of the appliance. In addition, such drive trains are rather noisy in operation due to the meshing gears or the chain engaging with the sprocket wheels.
Moreover, there are not only difficulties in accommodating the drive train elements in the cutter head, but there are also restrictions in accommodating the tooling rotors within a limited functional area and using the available surface of the tooling head for the tooling rotors as effective as possible. Due to the circular cross-section of the tooling rotors allowing rotation thereof, the tooling rotors cannot occupy the entire surface, but need spacing therebetween where there is no tooling effect. In other words, due to the round shape of the tooling rotors, the ratio of the surface area covered by rotors to the surface area not covered by rotors is rather small what results in a restricted tooling efficiency. For example, shaver heads provide for the shaving action only in those areas of the functional surface of the cutter head where there is indeed a rotor, whereas the spacings between the rotors cannot provide for any shaver action.
In addition to such efficiency restrictions, it is difficult to position the tooling rotors to fit with different surface contours to be treated. For example, if the tooling rotors of a shaver are positioned within a common plane, i.e., with their front surfaces in one plane, only those areas of the face having a substantially plane contour can be shaved using all tooling rotors, whereas in other areas of the face such as the chin only some of the tooling rotors contact the skin, whereas others do not. So as to relieve this problem, it has already been suggested to allow for some tilting movements of the tooling rotors to better adapt to the surface contour to be treated. However, such movability of the tooling rotors in addition to the rotation thereof necessitates more complex drive trains and hitherto, such movability could not sufficiently fulfill the need for better adaption of the rotor field to the surface contour to be treated.
For example, EP 15 87 651 B1 shows an electric shaver having three cutting rotors driven by an electric motor via a drive train having a central gear wheel which, on the one hand, is driven by a pinion connected to the motor shaft and, on the other hand, drives three output gear wheels connected to the cutting rotors via output shafts. Although there are only three cutting rotors, there is quite some space needed in the cutting head to accommodate the various gear wheels of the drive train.
A similar electric shaver is shown by EP 17 61 367 B1, wherein each of the cutting rotors is connected to the output drive shaft by means of a sort of ball and socket joint allowing for tilting movements of the cutting rotor, wherein viscoelastic elements are provided for elastically urging the cutting rotors to the skin surface.
An electric shaver having more than three cutting rotors is known from CN 101041237 A, wherein a plurality of cutting rotors are positioned along a circle around a central cutting rotor so that in total seven cutting rotors are arranged on the cutter head surface.